block 4-barn owls Flashcards
(25 cards)
what behavioural abilities should barn owls have?
-Must be able to locate prey accurately in both the:
- Horizontal plane (azimuth)
- Vertical plane (elevation)
what did Roger Payne find?
- late 1950s
-Sound is the cue that owls use. not body heat or odour
how accurate are barn owls
- 1-2 degrees in both azimuth and elevation.
- Similar to humans in azimuth but 3-fold better in elevation!
- Needs both ears…
how sensitive are barn owls?
- Most sensitive to sounds coming from the front.
- Most sensitive to high frequencies (think mouse in rustling leaves!)
- Can DETECT sounds ranging from 100 Hz - 12 KHz. similar to humans
- Can LOCALISE prey well between 1 - 9 KHz (for azimuth) and 3 - 9
KHz (for elevation).
What physical features enable an owl to pinpoint sound?
Face shape= channels sounds into the facial area e.g. like a satellite dish
-ears stick out but there’s a asymmetry.= one ear higher than the other and sounds can go in from the ear higher up and lower down too
-the facial ruff:stiff feathers in tightly packed rows funnel sound into the ears
-facial dish= the whole face
why might the barn owl evolved to use sounds cue?
- catch camolague/hidden prey
-They are nocturnal = an animal that is active at night and sleeps during the day.
ears of barn owls?
Asymmetric Ears
Left ear higher, points down,
Right ear lower, points up,
-therefore, blocking one ear createsan error in elevation and not in azimuth as expected .e.g. if we bloack the left ear the sound would seem to be coming hgher up.
If one ear of a barn owl is plugged so that the
sound intensity on that side is reduced, what
will happen sound localisation ability?
- barn owl has errors in elevation but there is also a small influence on localisation in azimuth.
.because of the ears point in different directions. right ear =up left ear= down e.g. if you block the left ear sounds seems to be coming from lower down and right higher up. - Experiments demonstrate that barn owls use Interaural
Intensity Differences IID (also known as Interaural Level
Difference (ILD) to determine the Elevation of a sound
source.
-
what do owls use to determine the azimuth(horizontal location)- SUMMARISE AND CHEAT SHEET KEEP FORGETTING
Key Cue: Interaural Time Difference (ITD)
This is the difference in arrival time of a sound between the left and right ears.
Because the ears are spaced apart, a sound coming from one side will reach the closer ear slightly earlier than the farther one.
⏱️ Two Types of Temporal Disparity
Transient Disparity (Onset Disparity)
The initial difference in the time it takes for a sound to start at one ear vs. the other.
It helps detect sudden sounds, like a twig snapping.
Ongoing Temporal Disparity
The continuing difference in the timing of sound waves between the two ears as the sound persists.
This is the main cue barn owls use to determine azimuth for ongoing sounds.
It’s especially useful for continuous or tonal sounds like a mouse rustling in leaves.
-see lecture for picture
what did the experiments show about azimuth?
Researchers placed earphones in owls’ ears and controlled ITDs very precisely.
They found:
Owls turned their heads accurately using ongoing temporal disparities.
They could detect ITDs as small as 10 microseconds — extremely precise.
How does the owl analyse Interaural Intensity
and Interaural Time differences based biologically?
Inner Ear
The basilar membrane in the cochlea performs frequency analysis.
Hair cells on specific regions respond to specific sound frequencies.
Auditory Nerve
Neurons connected to hair cells send frequency-specific signals to the brain.
These signals carry timing information, which is compared between ears.
Brainstem (e.g., Nucleus Laminaris)
Specialized circuits compare the timing of inputs from both ears.
This allows the owl to detect tiny differences in arrival time, giving it directional (azimuth) information.
what about ILD and ITD?
ILD = Interaural Level Difference (difference in loudness between ears)
ITD = Interaural Time Difference (difference in arrival time between ears)
This sentence is saying:
In the auditory nerve, there aren’t separate neurons for timing vs. intensity.
Instead, each individual sensory neuron carries both:
Timing info (when the sound arrived)
Intensity info (how loud the sound was)
So, at this early stage:
ITD and ILD are mixed together in the same nerve fibers.
It’s only later in the auditory pathway (like in the brainstem) that this information may start to be processed more distinctly for localization.
what is the elevaltion and azimuth encoded by?
Intensity (elevation) is encoded by changing rate of action
potentials.
– Higher intensity = more action potentials (spikes)=higher the sound was
Timing (azimuth) is encoded by phase locking of action potentials. =a neuron fires an action potential at a specific point in the sound wave’s cycle — like always firing at the “peak” of a wave.
why is phase locking important?
Precise Timing = Azimuth (Horizontal) Localization
The brain compares the timing of when the wave reaches each ear.
If the neuron fires at the same phase of the sound wave in both ears, the brain can measure the tiny difference in time the sound took to reach each ear.
That difference = Interaural Time Difference (ITD) = tells the owl which direction the sound came from.
Improves Accuracy
Phase locking gives extremely fine timing precision — down to microseconds in barn owls.
This is how owls can pinpoint prey in complete darkness.
Works Best at Low to Mid Frequencies
Phase locking is very precise for low and mid frequencies.
At very high frequencies, neurons can’t keep up with each wave cycle — phase locking breaks down.
what does each auditory neuron carry?
-each is specific for different frequency
-sound intensity is encoded by rate of action potentials
-sound timing is encoded by phase locking of action potential firing
what is parrallel processing of neuronal pathways in barn owls ?
Barn owls use both Interaural Time Differences (ITDs) and Interaural Level Differences (ILDs) to locate sounds in space. ILDs refer to the difference in sound intensity between the two ears, which helps the owl determine if a sound is coming from the left or right.
Parallel processing means that different neural pathways handle ILD and ITD information separately but simultaneously. This allows the barn owl to process spatial sound information quickly and efficiently.
where does the neuronal pathways occur in the barn owl
-on both sides of the brain=2 copies
describe the intensity pathway of prcessing ILDs ?-CHEAT SHEET
Sound Input Begins at the Angular Nucleus (NA):
Auditory nerve fibers (afferents) send sound intensity (loudness) information to the Nucleus Angularis (NA).
This nucleus processes how loud a sound is but does not track sound timing (not phase-locked).
Information Flows to the Posterior Lateral Lemniscal Nucleus (PLLN):
The PLLN receives two types of inputs:
Excitatory input from the contralateral Angular Nucleus (the opposite side of the brain).
Inhibitory input from the contralateral PLLN (the corresponding nucleus on the opposite side).
This arrangement allows the PLLN to compare the intensity difference (ILD) between both ears.
Since the Angular Nucleus does not track timing, the ILD pathway only processes loudness, not timing.
Neurons in the PLLN Are Organized to Detect Sound Intensity Differences:-CHEAT SHEET
Neurons in the PLLN are arranged in a structured way according to sound frequency.
Ventral neurons (lower in the nucleus) fire strongly when the sound is louder in the same-side ear.
Dorsal neurons (higher in the nucleus) fire when the opposite-side ear hears the sound more loudly.
describe the Time pathway for processing ITDs?-CHEET SHEET BUT KNOWWHAT IT INVOLVES
Nucleus Magnocellularis (NM): Receives sound; sends phase-locked (timing-preserved) signals to both sides of the brain.
Nucleus Laminaris (NL): Gets bilateral input from NM; contains delay lines and coincidence detector neurons.
Delay lines: Introduce timing delays so signals from each ear arrive at different times.
Coincidence detectors: Fire only when inputs from both ears arrive simultaneously.
Result: 5. Spatial Coding of ITDs:
Because each neuron responds to a specific time difference (ITD), and neurons are laid out in a physical order, the NL forms a map.
The position of the active neuron tells the brain where the sound came from (left, right, etc.).
- Fast and Accurate Sound Localization:
This setup allows barn owls to instantly and precisely locate where a sound is coming from, which is especially crucial for hunting in total darkness.
how do we turn timing information into place codes?-CHEAT SHEET
-– Each coincidence detector differs in its place in the laminar nucleus
giving an array for a given frequency band.
– Laminar neurons at the right end respond best to sounds from the owl’s left.
– Laminar neurons at the left end respond best to sounds coming from the
right of the owl.
– Laminar neurons in the middle will respond best to sounds coming from
the front (or the back) of the owl.
– They send signals up to the higher brain (ICX) where signals combine with
information on ILDs and from different frequencies to enable the owl to
pinpoint the sounds source
phase ambiguity-CHEAT
Phase ambiguity happens because sound waves repeat (they’re periodic).
If a signal from one ear is delayed or advanced by a full cycle, it still looks the same to the brain.
That means the brain can’t tell if the sound reached the right ear a little earlier, or if it was just a full wave behind.
This creates confusion: the same neural response could mean multiple different sound directions.
So the brain has trouble knowing the true source of the sound — especially for high-frequency sounds with short, fast-repeating waves.
Phase ambiguity is frequency-specific
Because each frequency has a different wavelength, a delay
that causes ambiguity at one frequency will not cause an
ambiguity for other frequencies
how can phase ambiguity be solved?- CHEET SHEET
The brain estimates sound location by combining signals from many coincidence detector neurons, each one sensitive to a slightly different frequency.
In the ICC (central nucleus of the inferior colliculus), neurons are tuned to very specific (narrow) frequencies.
➤ Because of this narrow tuning, they can suffer from phase ambiguity—where it’s unclear which direction the sound is coming from because the timing information is confusing or repetitive.
These ICC neurons then send their signals to ICX neurons (external nucleus of the inferior colliculus).
➤ ICX neurons receive input from many ICC neurons, each with different frequency tuning.
➤ This makes ICX neurons have broader tuning (less specific to a single frequency), which helps them resolve the phase ambiguity and pinpoint sound direction more accurately.
